Gallium-nitride (GaN) is a commonly used Group IIIA-N material for electronic devices, where Group IIIA elements such as Ga (as well as boron, aluminum, indium, and thallium) are also sometimes referred to as Group 13 elements. GaN is a binary IIIA/V direct band gap semiconductor that has a Wurtzite crystal structure. Its relatively wide band gap of 3.4 eV at room temperature (vs. 1.1 eV for silicon at room temperature) affords it special properties for a wide variety of applications in optoelectronics, as well as high-power and high-frequency electronic devices.
GaN-based HEMTs are known which feature a junction between two materials with different band gaps to form a heterojunction or heterostructure. The HEMT structure is based on a very high electron mobility, described as a two-dimensional electron gas (2DEG) which forms just below a heterostructure interface between a barrier layer (that typically comprises AlGaN) on a generally intrinsic active layer (that typically comprises GaN) due to the piezoelectric effect and a natural polarization effect. As with any power FET device, there are a gate, source electrode, and drain electrode, where the source electrode and drain electrode each include contacts that extend through the top barrier layer to form an ohmic contact with the underlying 2DEG in the surface of the active layer. One Group IIIA-N HEMT layout is a drain centered layout where the high voltage drain area is completely enclosed by the gate and by the source. This layout has advantages including regarding device isolation, edge termination, and leakage current control.